Characterization of a Legionella pneumophila gene encoding a lipoprotein antigen

Summary A prominent 19kOa surface antigen of Legionella pneumophila, cloned in Escherichia coli, was found to be intimatety associated with peptidoglycan. The DNA region encoding this antigen was mapped on an 11.9kb plasmid by means of detetion analysis and transposon mutagenesis. PhoA' gene fusions, generated by JnphoA insertions into this region, confirmed the presence of a gene encoding a secreted protein. PhoA' transposon insertions were also associated with loss of the 19 kDa antigen in immunoassays using a monoclonal antibody (mAb1E9) and the replacement of the 19kDa antigen with larger fusion proteins in immunoblots using Legionella immune serum. A 1540bp Psfl fragment carrying the gene was sequenced, and the open reading frame encoding the antigen was identified. The gene encodes a potypeptide 176 amino acid residues long and 18913 Da in size. The presence of a signal sequence of 22 amino acids with a consensus sequence for cleavage by signal peptidase II indicates that the antigen is a lipoprotein,